In situ infrared (FTIR) study of the mechanism of the borohydride oxidation reaction

Abstract

Early reports stated that Au was a catalyst of choice for the BOR because it would yield a near complete faradaic efficiency. However, it has recently been suggested that gold could yield to some extent the heterogeneous hydrolysis of BH, therefore lowering the electron count per BH, especially at low potential. Actually, the blur will exist regarding the BOR mechanism on Au as long as no physical proof regarding the reaction intermediates is not put forward. In that frame, in situ physical techniques like FTIR exhibit some interest to study the BOR. Consequently, in situ infrared reflectance spectroscopy measurements (SPAIRS technique) have been performed in 1 M NaOH/1 M NaBH(4) on a gold electrode with the aim to detect the intermediate species. We monitored several bands in B-H (nu ∼ 1180, 1080 and 972 cm(-1)) and B-O bond regions (nu = 1325 and ∼1425 cm(-1)), which appear sequentially as a function of the electrode polarization. These absorption bands are assigned to BH(3), BH(2) and BO species. At the light of the experimental results, possible initial elementary steps of the BOR on gold electrode have been proposed and discussed according to the relevant literature data.

The electrooxidation of borohydride: A mechanistic study on palladium (Pd/C) applying RRDE, 11B-NMR and FTIR

“…The reaction mechanism following proposed Reaction (21) would show a hydrogen oxidation at the ring above 0.00 V vs. RHE while Reaction (22) should show oxidation currents only at higher ring potentials. In case of Reaction (21) the evolved hydrogen could be further oxidized in an intelligent three dimensional electrode architecture [14,28]. At thin films on RDEs hydrogen bubbles are swiped away and lost.…”

“…In Table 2 the corresponding IR bands which are used for the interpretation of the results are summarized [12,20,21]. At this point we want to draw attention to the fact that IR bands from electrochemical in-situ IR measurements are influenced by the catalysts' surface [12].…”

“…While reaction intermediates are widely investigated for platinum catalysts utilizing online electrochemical mass spectrometry [19] and FTIR [20,21] there is little comparable data for Pd/C available.…”

Electrochemical impedance spectroscopy study of borohydride oxidation reaction on gold—Towards a mechanism with two electrochemical steps

“…In that context, more fundamental study of the BOR mechanism appears mandatory, so that the limiting steps of the reaction are isolated. As the BOR is very complex (numerous reactions pathways are possible), it is wise to measure directly the nature of the reaction intermediates from coupled techniques, for example in situ Fourier transformed infrared (FTIR) spectroscopy [41,42] or mass spectrometry (MS) [20]. Such measurements should serve as experimental benchmarks to be used for ab initio calculations, as recently undertaken by Rostamikia and Janik [43,44].…”

“…[19,22,37] for BH 4 − oxidation or [19,46] for BH 3 OH − oxidation), following gold surface oxide formation (OH − adsorption [46]), which was successfully modeled with an EAR step [37]. At the potential of the Au deactivation region, a so-called "film" of boron-oxide forms, probably due to polymerization of BO x species at the oxide-covered electrode surface, as detected by in situ FTIR on Au [41,42] and previously mentioned for Ag [17] or Pd and Ni [18] materials. This film negatively impacts the reaction [40] because it irreversibly modifies the electrode state of surface and prevents any reproducible measurement [45].…”